usb or hdmi for custom lcd controller

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mirth
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usb or hdmi for custom lcd controller

Post by mirth » Mon Mar 30, 2015 4:34 am

I want to build a custom controller for a very old lcd (for general use). That should be the hard part. But that doesn't worry me too much. The getting the data from the computer does. Since many people around here spends lots of time the other way; talking go controllers...

What is a nice way to get a screen buffer to my controller? Looks like USB and HDMI are my only options? And both look troublesome. Note: the lcd is 640x400x4 x60hz monochrome.

USB: seems to be proprietary and almost undocumented..
HDMI: just for starters; the spec says "supports any resolution" then "must support 640x480x60hz" then defines ntsc which is smaller (but bigger than real ntsc). And there is no Monochrome colour space? And the receiver chips all seem only to output lvds (way too new, but maybe...).

I have 2 choices on my end:
- Preferred: my mcu talks to the existing lcd controller (old enough to have childern of its own - the spec sheet shows connections for a z80.)
- Row/column direct, but... I'd need a lot of control over timing. And the ancient lcd will blow up if I treat it badly.

So which is less evil way to get video data I can use: USB or HDMI?

The goal is custom hardware only. The fallback is that plus modeline. Kernel patches are out because that's ugly.

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dekarl
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Re: usb or hdmi for custom lcd controller

Post by dekarl » Mon Mar 30, 2015 1:11 pm

mirth wrote:Since many people around here spends lots of time the other way; talking go controllers...
What is a nice way to get a screen buffer to my controller?
I don't think you'll get many answers here. The project sounds like its more of a hardware tinkering project that would go well with Raspberry Pi tinkering. I'd try asking over there.

mirth
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Re: usb or hdmi for custom lcd controller

Post by mirth » Mon Mar 30, 2015 1:48 pm

Then I asked badly. Is there documentation for USB display protocol? It doesn't seem to be in the USB spec. (My task, unlike Mythtv, is to write a client not a host).

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dekarl
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Re: usb or hdmi for custom lcd controller

Post by dekarl » Tue Mar 31, 2015 5:39 pm

mirth wrote:Is there documentation for USB display protocol? It doesn't seem to be in the USB spec.
I could not find a definition of a graphics interface, only monitor control and text on graphics display stuff.
But there appears to be a DisplayLink Community that is developing Linux support for their USB display interface chips. Maybe they know more.

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